A nondestructive testing using radiation is used in a wide range of fields from industrial use to medical use. For example, X-rays are electromagnetic waves having a wavelength in the range of approximately 1 pm to 10 nm (10−12 to 10−8 m). Among such X-rays, those having shorter wavelengths are referred to as hard X-rays, and those having longer wavelengths are referred to as soft X-rays.
An absorption contrast method using the difference in transmittance of X-rays transmitted through a test object is put to practical use in security related fields, such as internal crack inspection performed on steel and baggage inspection, by applying the high penetrative power of X-rays in the absorption images acquired using the method.
For a test object that is constituted of materials having similar densities and having less contrast due to X-ray absorption, X-ray phase contrast imaging that detects a shift in the X-ray phase due to the test object is effective.
As one type of X-ray phase contrast imaging, an X-ray imaging apparatus that uses a splitting element divides an X-ray beam and that includes a mask to block the X-ray beam at the edges (borders of pixel) of the pixels in a detector is disclosed in PTL 1. In this apparatus, units are set such that an X-ray beam is incident on part of an X-ray shielding mask when the test object is not present. Then, when the test object is disposed, the X-ray beam is refracted at the test object, and the position of the X-ray beam incident on the X-ray shielding mask changes. Since the amount of X-ray blocked by the X-ray shielding mask changes in response to the amount of displacement of the X-ray beam, the refraction at the test object can be detected as a change in the X-ray intensity. As a result, it is possible to detect an X-ray phase shift due to the test object.